There exist various processes for directly producing a non-woven material from a fluid dielectric substance, in solution or molten, by means of forces created by an electrostatic field on this substance.
One of these processes consists in wetting an electrode with a solution of the product intended to yield the non-woven, and forming an electrostatic field between this electrode and a second electrode, so as to atomise this solution and collect small fibers on the second electrode. The electrode wetted by the solution is in the form either of a toothed wheel so as to concentrate the electrostatic field on these points, or of a ring formed by a conductive wire. In both cases, the electrode is driven to rotate around a horizontal axis of rotation and its lower part passes down into the solution so as to wet the electrode as it rotates.
The yield from this process is low insofar as about 80 to 99% of the substance atomised in the electrostatic field is constituted by the solvent. Moreover, the devices for putting this process into operation only allow very small quantities of solution to be atomised. Finally, the width of the non-woven product obtained from such a device is necessarily reduced. It has been proposed to put several co-axial rings in parallel. However, such a solution gives rise to problems relating to the homogeneity of the non-woven product.
British Pat. No. 1,484,584 describes another process starting with a thermoplastic dielectric substance, which is melted and brought into an electrostatic field. The advantage of this process resides in the fact that it makes it possible to produce fibers without the use of a solvent and that a plurality of fibers are formed simultaneously from a layer of the molten substance. Consequently, its yield is greater than that of the above-mentioned process. However, the means for carrying out this process, constituted in particular by an endless wire electrode driven so as to move along its closed trajectory, has a limited interest from the industrial point of view because of the width of the product which can be obtained and the speed of production.
Moreover, in that Patent, the formation of the layer of molten material on the surface of the wire electrode is obtained by the passage of this electrode through a mass of molten material placed in a container, the opposite sides of which are pierced with respective openings so as to permit the wire to pass through this container and to leave it covered with a layer of molten material extruded through the outlet opening for the wire. On leaving the container, the extruded matter covering the electrode is subjected to the electrostatic field and a plurality of fibers are formed along the layer of this material. The centering of the wire electrode in the outlet opening controls the regularity of the thickness of the layer surrounding the electrode and, to a great extent, the quality of the fibers obtained. Moreover, the even heating of a large mass of molten material is difficult to achieve. The difficulty in obtaining a perfect centering of the electrode and the even heating of the material is no doubt one of the causes of irregularities found in the non-woven product obtained by means of this device.